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 ###Instrução: Qual é a data de construção para a Classe PRR gf30a?
 ###Tabelas: CREATE TABLE 1937 (1937_id AUTO_INCREMENT PRIMARY KEY, Title VARCHAR, Series VARCHAR, Director VARCHAR, Production Num. VARCHAR, Release date VARCHAR) CREATE TABLE 1980–1989 (1980–1989_id AUTO_INCREMENT PRIMARY KEY, January VARCHAR, February VARCHAR, March VARCHAR, April VARCHAR, June VARCHAR, July VARCHAR, August VARCHAR, September VARCHAR, October VARCHAR, November VARCHAR, December VARCHAR) CREATE TABLE wisconsin_counties_ranked_by_per_capita_income (wisconsin_counties_ranked_by_per_capita_income_id AUTO_INCREMENT PRIMARY KEY, County VARCHAR, Per capita income VARCHAR, Median household income VARCHAR, Median family income VARCHAR, Population INT, Number of households INT) CREATE TABLE general_electric (general_electric_id AUTO_INCREMENT PRIMARY KEY, PRR Class VARCHAR, Builder’s Model VARCHAR, Build date VARCHAR, Total produced INT, Wheel arrangement VARCHAR, Service VARCHAR, Power output VARCHAR) CREATE TABLE july (july_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Opponent VARCHAR, Score VARCHAR, Loss VARCHAR, Attendance VARCHAR)  
SELECT Build date FROM general_electric WHERE PRR Class = gf30a